Understanding Assignment Operators and Increment/Decrement in C++

1. Chapter 3.1 & 3.2 • Programming • Assignment Statements • Incrementing & Decrementing • Math Library Functions

2. Review: Assignment Operator The assignment operator (=)causes the operand on the left to take on the value to the right side of the statement. • This operator assigns from right to left. • Syntax: variable = value • valid invalid riker = 5.6 5 = riker *

3. Assignment Example 1 sum • #include <iostream> • Using namespace.std; • void main(void) • { • int sum; • sum = 25; //initialize sum • cout << “The number stored in sum is " • << sum; • sum = sum + 10; • cout << "\nThe number now stored in sum is " << sum<< ‘\n’; • } 25 35

4. Example 1: Output • Output: • The number stored in sum is 25 • The number now stored in sum is 35 • No surprises

5. Assignment Example 2 • int sum; • sum = 0; • cout << "\nThe value of sum is initially set to " << sum; • sum = sum + 10; • cout << "\nsum is now " << sum; • sum = sum + 20; • cout << "\nsum is now " << sum; • sum = sum - 30; • cout << "\nsum is now " << sum; • sum = sum - 40; • cout << "\nThe final sum is " << sum;

6. A Trace of Ex2 Assignment Example 2 Sumcout ??? 0 0 10 10 30 30 0 0 -40 -40 • int sum; • sum = 0; // initialize sum • cout << "\nThe value of sum is initially set to " << sum; • sum = sum + 10; • cout << "\nsum is now " << sum; • sum = sum + 20; • cout << "\nsum is now " << sum; • sum = sum - 30; • cout << "\nsum is now " << sum; • sum = sum - 40; • cout << "\nThe final sum is " << sum;

7. Example 2 - Output • Output: • The value of sum is initially set to 0 • sum is now 10 • sum is now 30 • sum is now 0 • The final sum is -40 Hopefully, no surprises here either

8. Assignment Operators Surprise! • A shorthand notation for certain assignments. • They all have right-to-left associativity. • MyVariable += TaxRate * Cost • variable op= (expression) • is equivalent to • variable = variable op (expression) MyVariable = MyVariable + TaxRate * Cost

9. Assignment Operators • += add then assign • -= subtract then assign • *= multiply then assign • /= divide then assign • %= modulus, then assign • X -= 3 º X = X - 3 • pay *= 0.35 º pay = pay * 0.35

10. Assignment Operators+= -= *= /= %= Assignment Operators • 1. i += 2 i = i + 22. r *= 7 r = r *73. j *= (k + 3) j = j * (k + 3) • 4. x /= y - 4 x = x /y - 45. hour %= 12 hour = hour % 126. left -= t_out left = left - t_out * *

11. Common UseAccumulating Subtotals Syntax:variable = variable + new_value; • Examples year_pay = year_pay + pay; balance = balance - debit; counter = counter + 1; counter += 1; }same *

12. Increment/Decrement • ++ increment-- decrementSurprise again! • unary operators take a single operandnum++, num--++num, --num

13. Increment/Decrement • k = k + 1 k = k + 3 • k += 1 k += 3 • k ++ no equivalent

14. Increment/Decrement num = num - 1num-- i = i - 1i-- • num = num + 1num++ • i = i + 1i++ num += 1 num -=1 i += 1 i -= 1 * * * * *

15. Increment/Decrement • value after executionk g1. k = 7;2. g = 2;3. k = g;4. g = g + 1; 7 %#@$ 7 2 2 2 2 3 or combine 3 & 4 k = g++ Use it first, then add 1 * * * * *

16. Increment/Decrementpostfix: first use it, then alter value count = 10;k = count++;cout<<k<<‘\t’<<count; k count 10 11 • z = 10;v = z--;cout <<v<<‘\t’<<z; • v z 10 9 * * * *

17. Use Before Increment/Decrement • output • 1cout << cnt++<<'\n'; • 2 cout<<cnt<<'\n'; • 3 cout<<(cnt++==guess)<<'\n'; • 4 cout<<cnt<<'\n'; • 5 cout<<cnt++<<'\n'; • 6 cout<<cnt<< '\n'<<'\n'; int cnt = 10, guess = 11; 10// print then inc 11 1// check then inc 12 12 13 * * * * * *

18. Use After Increment/Decrement • output • 1 cout << ++cnt<<'\n'; • 2 cout<<cnt<<'\n'; • 3 cout<<(++cnt==guess)<<'\n'; • 4 cout<<cnt<<'\n'; • 5 cout<<++cnt<<'\n'; • 6 cout<<cnt<< '\n'<<'\n'; int cnt = 10, guess = 11; 11// inc then print 11 0// inc then check 12 13 13 * * * * * *

19. int j = 5; Increment/Decrement a) 5 b) 6 c) 19 d) 0 e) 50 f) -1 g) 10 h) 6 • a) cout << j++ • b) cout << ++j • c) cout << j += 14 • d) cout << j /= 10 • e) cout << j *= 10 • f) cout << j -= 6 • g) cout << (j = 5) + j • h) cout << (j == 5) + j * * * * * * * *

20. Math Library Functions • cmath • sqrt(n) fabs(n) cos(n) • log10(n) log(n) • pow(b, n) etc. #include <cmath> Function prototypes (or declarations) * * *

21. Math Library Functions • name of the function • what it does • data type of argument • data type of returned value The actual function (object code) in usr/lib/libm.h g++ calculator.cc -lm Do not have to use

22. Math Library Functions • Ex. sqrt(49) pow(2.1, 3) • abs(-34.5) cos(30) • abs(34.5) Syntax:function_name (argument); *

23. Math Library Functions • sqrt( pow( fabs (-4), 3) ) = • sqrt( pow( 4.0 , 3) ) = • sqrt( 64.0 ) = 8.0 nested functions You can use returned values from functions in any expression cout << sqrt(64.0); value = 23 * sqrt(number) + 5; * * *

24. Type Casting • The explicit conversion of a value from one data type to another. Syntax:data_type (expression) int (5.34 * 1.68) int (8.9712) This returns a value of 8. * *

25. Type Casting • someInt = someDouble - 8.2; • someInt = int(someDouble - 8.2); • These are identical statements. * *

26. Type Coercion • The implicit (automatic) conversion of a value from one data type to another. someDouble = 42; is stored as 42.0someInt = 11.9; is stored as 11 g++ warning *

27. Common Programming Errors • not declaring all variables • storing data of one type in a variable of a different type. The variable data type is kept. • using a variable before assigning it a value • mixing data types in an operation • in integer division 4/5 = 0

28. MoreCommon Programming Errors • forgetting << and; • not initializing variables before use • applying ++ or – incorrectly

29. dummy box for extra sound “Sleeping is not a waste of time.” Deepak Chopra “Except in C++ class” Joseph DeLibero